1. Field of the Invention
The present invention relates to a pixel unit and an image sensor.
2. Description of the Related Art
Solid-state image sensors such as a Complementary Metal Oxide Semiconductor (CMOS), etc., can be manufactured by using a manufacturing process of a typical semiconductor, and analog circuits and digital circuits can be mixed on the same chip. Therefore, a significant advantage can be attained in that peripheral integrated circuits (IC) can be reduced.
This kind of solid-state image sensor is formed of a pixel part in which a plurality of pixels are disposed, and peripheral circuits are disposed on the periphery of the pixel part. Each pixel includes a photoelectric conversion element of a photodiode (PD), a floating diffusion (FD) for converting electric charges, which have been subjected to photoelectric conversion, into a voltage, and a pixel transistor including various transistors.
The FD includes an FD diffusion layer (or a diffusion region), FD wirings, and a gate capacitance of an amplification transistor. It is known that the capacity of the entire FD affects the voltage conversion efficiency. For example, there is known a structure in which a high concentration region of FD diffusion is separated from the separation end, for the purpose of improving the conversion efficiency of the solid-state image sensor (see, for example, Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013-225774